1. Field of the Invention
The present invention relates to the provision of a bond pad for effecting through-wafer connections to an integrated circuit or electronic package, and wherein the bond pad includes a high surface area aluminum bond pad in order to resultingly obtain a highly reliable, low resistance connection between bond pads and electrical leads. In particular, the invention is directed to the addition of an edge seal between the bond pad region and an active circuit region, and includes a crack stop, which is adapted to protect the arrangement from the entry of deleterious moisture and combination into the active regions of the chip containing bond pads.
In the current state-of-the-technology, through-wafer connections are frequently employed in the formation of advanced types of electronic packages, for instance, such as, but not limited to, 3D packaging, MEMS packaging, or CMOS imager packaging. In particular, the process which is utilized for these connections is designed to etch a via through the rear side of the wafer and through the bond pads, so as to expose the edges of the respective bond pads. Leads are then formed so as to connect the edges of the bond pads to solder bumps, which are arranged on the rear sides of the electronic package. Thus, for multilevel aluminum (Al) wiring, multiple levels are employed in order to form the connection between the leads and the bond pads so as to be able to obtain low resistance electrical connections. However, when employing (Cu) copper wiring, this particular approach is subject to a poor or relatively low degree of reliability in the use of multiple Cu levels to form connections between the bond pads and leads, as a consequence of oxidation and corrosion of the copper material. A single aluminum pad is frequently employed as a final metal layer in Cu interconnects processes.
More recently, in order to improve upon the technology, novel structure has been developed, as is described and claimed in copending U.S. patent application Ser. No. 10/904,677, filed on Nov. 23, 2004, entitled “High Surface Area Aluminum Bond Pad For Through-Wafer Connections To An Electronic Package,” which is commonly assigned to the present assignee, and the disclosure of which is incorporated herein by reference in its entirety.
That particular structure, as detailed in the above-mentioned copending application, may employ a single aluminum pad, but increases the surface area of this pad by forming via bars of either W (via bar width <2× the thickness of W) or W+Al (via bar width >2× the thickness of W) underneath the pad, or alternatively by adding metal on top of the pad.
Via bars can be readily formed using a standard via mask or by using an additional mask. The depth of the via bar can be enhanced in two ways: (1) through a use of RIE (reactive ion etch) lag to obtain a much greater etch depth for the via bar compared to the via, or (2) by using an additional mask to form the via bars before the vias. Hereby, the surface area can also be increased by using an isotropic etch of the dielectric which is selective with regard to the metal (dilute HF for SiO2 dielectric, O2 plasma for organic dielectric), so as to recess the edge of the package via with respect to the metal.
2. Discussion of the Prior Art
In essence, although this may be directed to various diverse components, said packaging arrangements, contamination and entry of moisture is encountered by the packages through either the rear or the side edges thereof, in which conventional crack stop and edge seals are ineffective in attempting to protect the chip when utilizing new packaging methods, such as those disclosed for devices as CMOS image sensors, including the known Schott package as described in the disclosure of “New Wafer-Level-Packaging Technology Using Silicon-Via-Contacts for Optical and Other Sensor Applications”, by Jürgen Leib and Michael Töpper in the 2004 Electronic Components and Technology Conference Proceedings, pages 843-847, and Shellcase package, as described in “An Innovative Approach to Wafer-lever MEMS packaging,” by D. Teomin, A. Badihi and G. Zilber (Shellcase Ltd., Manhat Technology Park) in Solid State Technology, V.45, n1; January 2002; pages 57-62. These packages access the bond pads from the rear or the sides of the wafer. As a result, the conventional crack stop and edge seal is not ordinarily adequate in protection of the chip when employing these new packaging arrangements and methods in the technology.
In the construction of other kinds of conventional devices, the crack stop and edge seals are also frequently inadequate to be able to preclude the entry of moisture and contaminating materials, which would adversely affect the functioning of the bond pads and the conventional electronics.
Moreover, the Shellcase packaging illustrates the crack stop and also the sealing or edge seal being arranged internally of the region of the bond pads, whereas in a Schott package, as known in the technology, a guard ring comprising a seal is arranged interiorly of the area surrounded by bond pads, the latter of which are then exteriorly encompassed by a guard ring.